Field of the Disclosure
The present disclosure relates generally to a locking spacer for a rotor blade. More particularly, the present disclosure relates to a locking spacer that is finally fitted in a dovetail slot provided on an outer circumferential surface of a disk put on a rotor shaft in the process of alternate mounting of a blade and a spacer in the dovetail slot.
Description of the Background Art
Generally, a turbine is a mechanical device that obtains torque by impulsive force or reaction force using flow of a compressible fluid such as steam or gas. It is called as a steam turbine when steam is used and a gas turbine when combustion gas is used.
A thermodynamic cycle of the gas turbine is the Brayton cycle, and the gas turbine is constituted by a compressor, a combustor, and a turbine. The operation principle of the gas turbine comprises the following four steps: compression, heating, expansion, and heat dissipation. That is, the air in the atmosphere is drawn first, compressed by the compressor, then sent to the combustor to generate high temperature and high pressure gas to drive the turbine, and the exhaust gas is discharged to the atmosphere.
The compressor of the gas turbine serves to draw air from the atmosphere and supply combustion air to the combustor, and the combustion air is subjected to an adiabatic compression process, so that the pressure and the temperature of the air are increased.
In the combustor, the compressed air is mixed with fuel and is burned under equal pressure to produce high energy combustion gas of high energy, and to increase efficiency, the combustion gas temperature is increased to the heat resistance limit that the combustor and turbine components can withstand.
In the gas turbine, the high temperature and high pressure combustion gas from the combustor is expanded, and it is converted into mechanical energy by applying the collision reaction force to rotating blades of the turbine. The mechanical energy obtained from the turbine is supplied to the compressor required to compress the air and the remainder is used to drive a generator to produce power.
Since the gas turbine has no reciprocating motion in major components, there is no mutual friction part like a piston-cylinder, whereby consumption of lubricating oil is extremely small, amplitude which is characteristic of reciprocating machine is greatly reduced, and high speed movement is possible.
In the turbine of the steam turbine and the turbine and the compressor of the gas turbine, a rotor shaft rotating at a high speed is supported by bearings, and a plurality of disks having holes in the centers thereof are inserted and fixed in the turbine shaft. A plurality of rotating blades is arranged along the outer circumferential surface of each disk. Turbine blades serve to convert high-temperature and high-pressure steam or combustion gas energy into rotary motion, while compressor blades serve to continuously pressurize the intake air.
FIGS. 1 to 4 are views showing a method of mounting a blade along the outer circumferential surface of a disk. The method is that the blade and a spacer are alternately fitted in a dovetail slot formed along the outer circumferential surface of the disk. A dovetail joint having a shape complementary to the shape of the dovetail surface is formed in the lower portion of the base of the blade and in the spacer.
Referring to the assembly process in FIGS. 1 to 4, with the blade or the dovetail joint of the spacer facing the circumferential direction of the dovetail slot, that is, with the dovetail joint angled at 90 degrees with respect to opposite sides of the dovetail slot, the blade and the spacer are inserted into the dovetail slot, and in this state, the blade and the spacer are rotated at 90 degrees angle such that the dovetail joint is fitted into the dovetail slot.
The dovetail joint of the blade and the spacer with respect to the dovetail slot has a slight clearance and gap in the radial direction so that the blade and the spacer can be rotated at 90 degrees angle in the dovetail slot, and a spring plate (not shown) is provided in a groove formed in the bottom surface of the dovetail slot so as to push the blade and the spacer out of the radial direction to bring the dovetail joint into contact with the dovetail slot. Since centrifugal force is applied on the blade and the spacer when the rotor shaft is rotated, the clearance and gap in the radial direction do not affect the operation of the turbine engine.
The blade and the spacer are assembled alternately in the dovetail slot one by one. The last assembled spacer cannot be engaged in the dovetail slot by rotating it at 90 degrees angle in the dovetail slot because the space remaining in the dovetail slot is exactly the same as the size of the spacer. Accordingly, the last assembled spacer should have a specific structure that can be assembled without being rotated in the dovetail slot. For this reason, the last assembled spacer is called a locking spacer.
Fundamentally, the locking spacer should be able to be engaged in the opposite sides of the dovetail slot without being rotated, and the assembly structure should be simple, robust, and easy to disassemble for maintenance.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the background art that is already known to those skilled in the art.